Sequence control



Jan. 11, 1949. R. D. COWHERD ETAL 2,458,683

SEQUENCE CONTROL Filed Jan. '7, 1943 3 sheets sheet 1 I0 I INVENTOR K05154 7 D. (UH HERD YW/L L 114M H. STA/IL JR.

ATTORNEY 1949. R. D. COWHERD ET AL 2,453;633

SEQUENCE CONTROL Filed Jan. 7, 1943 3 Sheets-Sheet 3 POSITION I IIDIDZIILIYHSZIIIIXXXI'XIIXIIIXN SWITCH-l4] LIMIT SWITCH ACTZ/ATOR- I40 SWITCH-I42 1 A y F h SW/TCH-748 Lg M744 U I SWITCH-74.9 CAM-[45 I I SWITCH-I5U 641M446 I I SWITCH-757 M447 mum/vs Pm. MIN. 0 .50 I50 200 250 550 400 450 .550 600 650 750 300 800' A A A A A A B PUMPSO/VLl/Vf B B B B B I I c c c c c c C .c I 0 D 0 0 0 0 0 D PUMP CAPALIUES PUMP 6.0M. A .50

B 1.50 C Z00 fiflfill y fi mfkD 0 400 BYW/LL/AMHSTAHLJR.

ATTORNEY Patented Jan. 11, 1949 2,458,683 I SEQUENCE CONTROL Robert D. Cowherd, Atlanta, Ga., and William H. Stahl, Jr., Water bury, Conn, assignors to The Bristol Company, Waterbury, Conn, a corporation of Connecticut Application January 7, 1943, Serial No. 471,620

1 Claim. 1

This invention relates to the control of a variable condition such as pressure, temperature, or the like. It has been specifically developed in conjunction with the control of a plurality of driving units, such as pumps or blowers, for maintaining a fluid pressure at a substantially constant value, and will be described with particular ref erence to such control by way of illustration.

It is the object of this invention to provide for the purpose set forth a control system in which the selection of the proper combination of controlled units will be automatically effected with a minimum of pressure variation.

It is a further object of the invention to pro vide means for effecting the desired control through the use of a simple form of pressure gauge having only a single set of contacts.

A further object of the invention is to provide a control system of the above nature in which the operating characteristics are readily adjustable.

A further object of the invention is to provide a control system of the above nature in which it shall be possible to add further controlled units with a minimum of modification in the original installation.

The invention further provides a control system of the above nature in which, if the pressure should reach the low control point and then rise to some point between the high and low values during a given period, the pump combination will not be changed.

It is a further object of the invention to provide a control of the above nature in which, if the pressure should reach the high control point and maintain this value for a period greater than a predetermined time interval, a selected pump or combination of pumps shall be cut oil the line, this action being repeated on other units until the pressure drops below said high control point.

Other features of the invention will be hereinafter described and claimed.

In the accompanying drawings:

Fig. 1 is a diagrammatic representation of a control system embodying the principles of the invention and adapted to the control of three separate centrifugal pumps feeding into a common main.

Fig. 2 is a diagrammatic representation of an alternative form of the control system embodied in the invention, and adapted to the control of a group of four pumps.

Fig. 3 is a diagram showing the relative conformation and positioning of certain control elements characterizing the form of the invention shown in Fig. 2.

Fig. 4 is a diagrammatic view illustrating a modification of the form of the invention shown in Fig. 2.

Referring now to the drawings: The numeral l0 designates a source of water supply from which one or more of three centrifugal pumps H, [2, and I3, driven by electric motors l4, l5, and I6 respectively, are adapted to pump water into a supply main H in which it is desired to maintain a constant pressure as determined by a gauge i8 connected to the main H by means of a conduit Hi. The movable pointer of the gauge l8 carries a contact 20 adapted to make electrical connection with an adjustable stationary contact 2| when the pressure measured by said gauge is below a predetermined value and with an adjustable stationary contact 22 when said pressure is above said value.

A relay 24 adapted to be actuated by a winding 25 has five sets of contacts; three, designated as 25, 21, and 28 respectively, normally open; and two, designated as 29 and 30, normally closed. Two relays 3| and 32 are provided, with contacts adapted to be opened upon energization of their actuating coils and closed upon deenergization of said coils. Three similar relays 35, 36, and 37 are provided with normally open contacts of sufficient capacity to carry the operating currents of the pump motors l4, l5, and I6, and adapted to be closed upon energization of their respective actuating coils. These may be motor starters of any conventional type.

A timing relay at of the instantaneous-reset type is provided with a constant-speed driving mally stationary contact 45 when the clutch is energized and the motor 42 running, and to reset instantlyto a fixed stop 46 when the clutch is deenergized. Associated with the clutch 43 is a contact 41 normally open, and adapted to be closed only for such time as the operating winding of said clutch is energized. The position of the stationary contact 45 can be set by means of an adjusting screw 48, so that the time lapse between energization of the motor and closing of the contacts can be varied through a wide range, and determined by the excursion of an attached pointer 49 with respect to a graduated scale 50.

A timing relay 5! of the instantaneous-reset type is provided with a constant-speed driving motor 52 acting through a magnetic clutch 53 to cause a contact 54 to be advanced to meet a normally stationary contact 55 when the clutch is energized and the motor 52 running, and to reset instantly to a fixed stop 56 when the clutch is deenergized. Associated with the clutch 53 is a contact 5'! normally open, and adapted to be closed only for such time as the operating winding of said clutch is energized. The position of the stationary -contact*55 *can be *setbymeans of an adjusting screw 58, *so that the time lapse between energization of the motor and closing of the contacts can be varied through a wide range, and determined by the excursion of anattached pointer 59 with respect to a graduated scale 60.

A stepping relay 6| includes -two contact arms t2 and 63, and a wheel 64-having*a plurality of notches evenly spaced about a portion of its periphery, said arms and wheel being fixed to'a common rotatable shaft 65. The Contact arm BZis adapted to engage stationary contacts sci-trans 68, and is so formed that as it is advanced from one of said'contacts to another,--thecontaots'fi'rst engaged remain in-thecircuit as =fi-1rther contacts are included. The contact arm 63 is adapted'to engage a stationary contact member-BS whenat one-limit of its travel, and toengage a stationary contact member -10 *when at the other-limit. Rotatably mounted-upon the shaft B5-is an arm H carrying a double-ended pawl 'element'lz pivotally mounted upon the extremity thereof, and ada'pted, when rotated through "a small angle about its mounting, to engage the notcheson thewheel 64 'to-rotate the same. Attached to the .ap'awl element 12 is an arm 13 radially disposed with respect to the arm 1l,'and'adapted when'defiected through a limited angle about the pivot-point oi saidpawl element to cause 'said' -element-to r'ock about its mounting on'the 'a'rmll -andto 'engage one or other of the notches "on the "wheel 64. Attachedt'othe pawlelement 12 15 91 weight 14 adapted to maintain the arms 11*an'd13 normally in line with each other and in a'verticallp'osition, with'the pawl element 12 'disengagedfro'mthe notches in the wheel "64,

Pivotally connected to the extremity-of "the air-m 13 is a rod '15 carrying two*oppositelytlisposed plungers I6 and 11 formed-of m'agneticniaterial and adapted to be acted upon-by solenoids ts' and "it respectively. The arrangement "or the mecha nism associated with the wheel 64 is suchthat upon energization ofthe'sole'noid 1-8 the-plunger '18 will be attracted, causingth'e arm='13--to 'r'otate the pawl element 12 througha liir'i'ited an'gle about its point of pivoting "on 'the arm ngw-ner eby said pawl element will be'caused to engage-one of the notches on the wheel 64. Upon con'tinued energi- -zation of the solen0id'18 the rerce appiiea to'the arm 13 will cause the arm 'H tobe rotated infa clockwise sense as shown in thedrawing-through a limited angle about the theshaft 65, and the wheel 64 to be moved througha 'similar'angle by virtue of its engagement with thepawl element 12. The parts of the stepping 'r'elaya'res'c "proportioned that a single increment or motion as communicated to the wheel 54 and the-shaft "65 by one impulse derived from the solenoid 18 will cause the contact arms'6'2 and63- to be advanced through a distance corresponding to the spacing between consecutive-stationary contacts engaged by said contact arm 62. The action of the stepping relay upon energization of the-solenoid '19 will be exactly similar to that set forth, 'butin a reverse sense.

A motor-operated interrupter 80 is provided with a single pair of contacts 8 l 'and 82,' and by means hereinafter to be set forth, is caused always connectionsby which the system -operat ive 'areas follows: A pair of conductors 85 r and 85,-connected through suitable protective fuse system is readily adaptable for use on alternatingcurrent supply, and in fact would in all likeli- -hooiiUbeused on such an installation, and that the pump'motorswould probably be adapted for use-on atpolypha'seelectric system. The electrical may be rendered links L- L to the main conductors 83 and 8%, provide negative and positive bus respectively for the connections of the control network. The eommon co ritact-m of the gauge-Wis connected to the .'positive bus"8 6; the low contact -21 of said -gauge-is' connected by means of a conductor-"81 to one side of 'the normally open contact 2'6 *a-nd one side of the normally closed --con tact 29 111 the relay -24; and the high contact -2'2-by means-of a'conductor-88-to one side of the normally open' contact 21 andof the normally closed-contact 30 inthe're'lay 2 l. The-free termina1of'contact26 is connected =by:a conduc- 't'or'-=89*to' one-end of the solenoid --18 inthe stepping relay =61; the free terminal of contact "2-1 is connected by means of -:a=conductor 0 to one end of the solenoid'19'in the stepping relay m; and the otherendsof said solenoids "are botirconriectedto the negative bus 8-5. The free terminal of'contact 29 in the relay -is connected *bymeans of a conductor 9| to'oneside oi the contact-of relay 3-! andthefree terminator contao'tfill in the relay 24- is'connectedbymeans pi a conductor 92to one'side=of the contact :of "relay =32. One side of the actuating coil 250i the relay '--24 is connected to th'enegative -bus==85, and the other side by-means of "a conductor 93' to' contact 8! of the interrupter 30. Contact 82 ofsaid interrupter is 'connected to'thepositive'bus BB. One

' conne'cte'd"by means of a conductor 98 to one endof the"electromagnetof the-clutch 43 in the timing relay' "4l,andalso to' on'e side of the contact actuated bysaid elect'romagnet. The/Tree terminal 'ofthe'- contact relay 32 is connected by means of' a conductor "9'! to'one'side cf the electromagnet of the clutch==53 in the timing i'e'lay 5l, and also to onesideofthe -c'ontact' 5'l -actuated by said 'el'ectrornagnet. "The free terminal of :the contact l'l in the timing rela'y d'l is' connected'by rn'ea'ns 'of a 'c'onductor efl to one side of the motor '42; the free terin-i'rial ofthe"contact 5'l in the timing relay 5! is connected by means of a conductor '99 to on'e side "of the motor 52 and the "free 'ter mi nalsof the motors' 42' and 52 'ar'idof the electroma'gnets inthe clutch 43 an'd 53 are all connected to the negative bus B5. The -movable contacts 14 ana -54 inthe timin'g' relays are i nterconnectedby meansof a con'ductor Hill, which 'fin turnis 'ccnnected t0 oneter minal' -of -'the contact 28 in the relay 24 and also tonne-terminal of the interrupter motor 80, the other terminal is one in I ing denergized the solenoids of said contact 28 being connected to the positive bus 86, and the other terminal of said motor to the negative bus 85.

Contact arms 62 and 63 of the stepping relay 6| are both connected to the positive bus 86. Contacts 66, 61 and 68 of said relay are connected by conductors IGI, I62, and I03 to one side each of the actuating coils of relays 35, 36, and 3'! respectively, the free sides of said coils being connected to the negative bus 85. One side of each of the contacts of relays 35, 36 and 3! is connected to the main positive conductor 84. The free side of the contact of relay 35 is connected by means of a conductor I04 to one side of the pump motor I4, the free side of the contact of relay 36 by means of a conductor I to one side of the pump motor I5, and the free side of the contact of relay 3'! by means of a conductor I66 to one side of the pump motor I6, the free terminals of said pump motors all being connected. to the ductor B3.

The connections of the system as described provide for the energization of the control circuits from the same source 83-84 as the pump motors; but by removal of the links L-L the two networks may be completely separated and adapted for energization from independent negative main consources.

For the purpose of explaining the operation 'of the control system it may first be assumed that the pressure in the supply main I1 is for the moment at the set value of the gauge I8, so that neither of the contacts 2| and 22 is engaged by the common contact 20, and also that the stepping relay is in the position shown in the drawing, with the contact arm 62 out of engagement with any of its cooperating contacts 65, 61, and 68, and the contact arm 63 engaging the contact 69. Under this condition the relays 35, 36, and 31 will remain deenergized, with their contacts open, so that no power will be supplied to the pump motors I4, I5, and I6, and these motors will remain at rest.

With contacts 2| and 22 both out of engagement with the contact no connection exists from the conductors 8'! and 88 to the negative bus 85, so that whatever position may be assumed by the relay 24, no circuit can be completed, through any of its contacts 26, 21, 29, and 30. Therefore, without respect to the position of the relays 3| and 32, the magnetic clutch coils 43 and 53 in the timing relays 4| and 5| will remain deenergized and the contacts 41 and 5'! opened. Thus, the motors 42 and 52 in said timing relays will remain at rest, and the contacts 44 and 54 will lie in their zero positions as determined by the stops 46 and 56. There being no engagement between the contacts 44 and 45 or between the contacts 54 and 55, no connection is established between the conductor I00 and the positive bus 86, so that the interrupter motor 86 will remain at rest. For reasons hereinafter to be set forth it will be seen that the only position in which the motor 80 can come to rest at the terminationof an operating cycle which the contacts 8| and B2 are separated. Under this condition the actuating coil of the ,relay 24 will be deenergized, and said relay will stand with its contacts 29 and 30 closed and its contacts 26, 21, and 28 opened, thus leav- IB and I9 of the stepping relay 6|. Contact arm 63 of the stepping relay 6| being in engagement with contact element 69, there will be provided a path whereby current may flow from the positive bus 86 through conductor 95 and the actuating coil of relay 32 to the negative bus 85, energizing said relay and opening its contact. There being no connection between conductor 94 and the positive bus, relay 3| will remain deenergized and will stand with its contacts closed.

With the foregoing description of the relationship of elements of the system in view, consideration may now be given to performance of the apparatus under the following typical operating conditions:

(1) Pressure below the low control point setting-no pumps running.

When the pressure in the conduit falls below the desired value, or range of values, the contact 26 in the gauge I8 will engage the low" contact 2|, completing a circuit whereby current may flow the positive bus 86 through the conductor 81 and the contact 29 in the relay 24, and conductor 9| through the closed contact of relay 3|, and conductor 36, to the actuating coil of magnetic clutch 43 in the timing relay 4|, and thence to the negative bus 85. Simultaneously with the actuation of the magnetic clutch 43 the contact 41 is closed, allowing the motor 42 to become energized and the contact 44 to be started from its position of rest toward engagement with the contact 45. No further action of the control system will take place while the contact 44 is in transit from its position of rest toward the set position of the contact 45. If during this interval the pressure as measured by the gauge l8 should for any reason rise to the set point, the contacts 20 and 2| will be separated, the actuating coil of the magnetic clutch 43 deenergized, and the contact 44 immediately reset to zero.

Should the low pressure condition be maintained during the established time interval of the timing relay 4|, the contact 44 will engage the contact 45, establishing a connection between the positive bus 86 and the conductor I60, whereby the motor of interrupter will be energized and the contacts 8| and B2 brought into intermittent engagement. The first engagement between said contacts BI and 82 will permit current to flow from the positive bus 86 through the conductor 93 and the actuating coil 25 of the relay 24 to the negative bus 85, thus energizing said coil and causing the contacts 29 and 36 in said relay to be opened and contacts 26, 21, and 28 to be closed. The closing of contact 28 will allow current from the positive bus 86 to pass directly through the motor of the interrupter 86 to the negative bus 85, thus bridging the contacts 44 and 45 in the timing relay 4|. The opening of contact 29 will deenergize the timing relay 4|, causing the contact 44 to be separated from the contact 45 and reset to its zero position. These contacts being bridged, however, by contact 28, their separation will not deenergize the motor of the interrupter 80, which motor will continue to run until it attains a position where the contacts 8| and 82 are separated, deenergizing the coil 25, allowing the relay 24 to revert to its original position, thus opening the contact 28 and deenergizing the motor of the interrupter 80 in a position where the contacts 8| and 82 are separated.

The closing of the contact gizatlon of the coil 25 provides a path for current from the positive bus 86 through the contacts 20 and 2| and the conductor 81, to the conductor 69,

26 during the enercausing an impulse "24, which in turn, through the contactsit, will to a position where it engages age-omen "and thereby through the-solenoid =1 3zin: the step- :ping relay 6i to thenegative bus '85.

be rotated first in a counter-clockwisesense 1 as seen in the drawing through-a small angle about the pivoting point of saidzpawl element untilaits right hand 'extremity engages one of the notches uponthe periphery of the wheel 64, inhibiting further rotation of the pawltelement 12. Con ltinuation of the force upon the rod 115 will cause the arm H to be rotated about the axisof'shait 65, and the wheel fi lto be similarly rotated ina clockwise sense as seen in the drawing, causing the shaft 65 to be angularly displaced, the arm 63 to be cleared from the contact =element 69 and the contact armfill brought into engagement with the contact element 66. Upon'release of therelay 2a the solenoid "i8 will-be deenergizedand the pawl mechanism will revert to position, leaving the contact arms63 and Min their displaced positions.

Separation of contact arm at fromcontact-element 69 will cause the relay 32-to be deenergized and its contacts closed. Engagement of thecon tact arm 62 and the contact element tfi willprovide a path for current from the positive'bus llii through the conductor 'HJ! and the actuating coil of relay 35 to the negative bus 85, thusclosing the contacts of relay 3 to pass from the main positive conductorild and the conductor 94 to the pump motor It and thence to the main negative conductor 83, whereby said'motor will be energized and the pump 15 placed in service.

(2) Pressure remaining elow the low control point-one pump running Immediately upon the deenergization of relay 2d during the starting cycle of the pump l-I, the contact 29 will be closed; and, should the-contacts 26 and 2! in the gauge lBstillbedn engagement, the timing relay H-will have a second cycle initiated, and the contact will again approach the contact 15 as in the previousinstance. Should the pressure as measured bythe gauge l8 fail to rise sufficiently to disengage contact "it from contact 2| during the timing interval established by the setting of the relay 4l,the contacts of said timing relay will be-closed, energizing as before the motor of the interrupter 86* and to be imparted to the relay T8 of the stepping relayti armB-Z advanced both the contact elements 66 and 61', thus energizing the relay "353 and bringing into action the pump [2 in addition to pump H which is already on the line.

(3) Pressure remaining below the low control point-two pumps running Should the united efforts of pumps and l2 be insuflicient to raisethe pressure above the low control point, the contacts '20 and 2! will remain in engagement; and should such a condicause the solenoid I to be energized and the contact 'tion'be maintained over a'time interval repre sented by the setting of relayAL-the starting cycle as above will :be repeated, and "pump 13 its original and allowing current automatically put in service on the line. Upon the advancing of the shaft 65 in the timing'relay 'Bl to the final'positioir -which corresponds 'to engagement of the contact armfiz with'.theicontact element 68, the'contact arm 63willbe 'broug'ht into engagement with the contact element 'm, 1

-causing=-relay 3i :to'beienergized and rto-z open its contacts, whereupon there no longer; anyscomplete circuit between the contact/.29iinn-the relay =25 and the energizing coilrin the timing. relay dl.

Thus, :even should the contacts :29 auditor the gauge 18 remain together, no further aotionuof the control mechanism canwtakejplace.

(4) "Pressure comes within control zone starting cycle pointed out under condition 1- above,:should -the=. pressure rise abovethe slow .controlpoint durring. the. time interval .oflthe relay! 1 the as "establishediby thesetting actuatingcoil of zthesclutch :43 will bedeenergized before the contact G l-comes .into engagement with the contact @5; :and'lthe timing relay will-be re-set withoutthe starting or further pump motors.

(5) Pressmeuttains 'high conta'ctsetting When the pressure exceeds a desired value, or range of values, contact 20 of gauge I8 is brought :into engagement with the ih-igh contact .22,

whereby current may flow from the positive .bus .86 through the. conductor 88 the contacts 30 i, in the relay 2-4, the conductor (92, the-contactsiof relay -32, conductor 91 and the-:actliating .-coil -of .magneticclutch-it to the negative bus 85. Errorgization of the clutch magnet will also close-.the

-.contact .51, causing the motor "52 to the started similar to the hereinabove described :operation'oi the relaynl, the motor-=- of the 'interrupter-zflflvwill be :started, the contacts Bi and :82 imomentarily rclosed. andv the actuating coil 15: of the l relay :24

. energized. Actuation of the relay F.2d willealise the :contacts. 30 .to be openeduandrthe contacts .21 to be closed, whereby, through'zconductorailfl, the solenoid 19 of the. stepping relay :tl :wilhbe; energizedlan di theishafti 6:5 rotatedthroughcone incre- ;ment inaa; sense opposite to that:eassociatedvwith i lowxpressure; separating; contactarmetZ fromwt'he contact elementwfifl, deenergizing: the relay-stand cutting the-pump t3 out :of service.

f ShOul'dJthe'. pressure :continue attherhight valne "after-stoppage. oi :thepump l3, theicy'cle as. above willbeirepeated, and-pump l2 shut downpand, upon further :continued "maintenance .of :high pressure for an iritervalsexceedingthe-se'tting of the timing "relay-B l the -pump H willbe: removed from-service.

It will be 'seen that there has thus been provided a system adapted .tothe 'con'trol of "a" plurality of pumpspw-hereby, w'ith -a minimum of "variation of pressure-from a'pre'deterinined-set value, selection-Will be made of a group of -pumps best suited to the-maintenanceof saidpressure. By selecting the pumps to have *s-uitably flat "characteristics; and-combining-pumps of suitable 'relative'capa'cities, it *wi-ll-be'possible to operate *the system at a maximumdeglee of efficiency through an extremely'wi'derange of demand'values. 'The'adjustabletiming features-of the'relays 4i and5iprovide-for'transient conditions, "eliminating erratic operation in the event of surgesin the system,'-and also giving timefor any particular pump or" combination to establish "a* steady condition, before initiating further ac- 'tion-onthe part of the 'control elements.

In-Fig; 2 :is showman-alternative" form ofcom trol embodying the principles of the invention and including a time-cycle-control instrument, whereby there is made possible a wide variety of pump combinations suited to the demands made upon the system. Four pumps A, B, C, and D of capacities hereinafter to be set forth, are arranged to be driven by motors I24, I25, I26, and I21 respectively, for the purpose of transferring a liquid from a source of supply I28 to a conduit I29 in which it is required to maintain within specified limits the pressure as measured by a controlling pressure gauge I30 connected to the conduit I29 by a tube I3I. The gauge I30 is provided with a common contact element I32, movable in response to changes in the measured pressure and adapted to engage an adjustable stationary contact I33 when said pressure falls be-- low a predetermined set value and to engage an adjustable stationary contact I34 when said pressure rises above said predetermined value.

A cycle control instrument I35 comprises a shaft I36 adapted to be rotated at a constant velocity by a reversible motor element I31 having two windings I38 and I39 adapted to operate said motor to rotate the shaft I36 in a clockwise and a counter-clockwise sense respectively, according to which of the windings I38, I39 iselectrically energized.

Carried by the shaft I36 is a limit switch actuator I40 adapted to separate normally closed contacts I4I or I42 according to which limit of its travel has been attained by the motor element I31. As shown in the drawing, the shaft I36 is standing in such a position that the limit switch MI is open and the limit switch I42 closed.

Mounted upon the shaft I36 are four cam elements I44, I45, I46, and I41, associated therewith electric switch elements I48, I 49, I50, and I5I respectively. The cam elements are provided with indentations and projections upon their peripheries, whereby said switch elements may be actuated to open or close their contacts in response to the angular positions attained by said cams. The relative positionings of the contour features of said cams are indicated in Fig. 3, and will hereinafter be more fully discussed.

In the interest of simplicity in outlining the wiring diagram, the system may, as in the form hereinbefore described, be considered as adapted for use on a two-wire power supply system having a positive bus I and a negative bus I56. The common contact element I32 in the gauge I30 is directly connected to the positive bus I55.

The low contact I33 is connected by means of a conductor I51 to one end of the winding I 38 of the motor I31, and the other end of said winding by means of a conductor I58 to the limit switch I42 and thence to the negative bus I56. The high contact I34 of the gauge I30 is connected by means of a conductor I59 to one end of the winding I39 in the motor I31 and the other end of said winding by means of a conductor I60 to the limit switch MI and thence to the negative bus I56. One terminal of each of the pump motors I24, I25, I26, and I21 is connected to the negative bus I56. The remaining terminal of the motor I24 is connected by means of a conductor I6I to the switch element I48 and thence to the positive bus I55. The remaining terminal of the motor I25 is connected by means of a conductor I62 to the switch element I49 and thence to the positive bus I55. The remaining terminal of the motor I26 is connected by means of a conductor having operatively cam shaft I36, together with all be open and the I I30 and the coil venting operation of the control mechanism should the pressure in conduit I29 rise above the 10 I63 to the switch element I50 and thence to the positive bus I55. The remaining terminal of the motor I21 is connected by means of a conductor I64 to the switch element I5I and thence to the positive bus I55.

For purposes of explanation of the operating principle of the control system, it may be assumed that the pumps A, B, C, and D have been selected to have normal capacities of 50, 150, 200, and 400 gallons per minute. By properly distributing the projections and depressions about the peripheries of the several cams in the instrument I35, it will be possible to operate these pumps in various combinations, so that the capacity of any pump or of any combination of pumps may be utilized and rendered available subject to the command of the contacting gauge I30. A typical shaping of the cams to effect such a purpose will be seen by reference to Fig. 3, in which is shown a development of the several cams including that which actuates the limit switches. With the arrangement given, it is possible to obtain fourteen significant positions of the cam shaft I 36, each position corresponding to a predetermined pump capacity suited to a particular demand for liquid handled.

The cam peripheries are represented in such a way that, line as shown in the diagram sponding switch is closed, and when the contour line is low the switch is open. Considering now the conformation of the individual cams, it will be seen that the limit switch actuator I40 (which for purposes of simplicity is shown as a single cam) is so conformed that switch MI, in series with the winding I39 of the motor I31, is open in the first position of the cam shaft and is closed in all other positions; while the switch I42, in series with the winding I38 in said motor, is closed in all positions excepting the last. In order to avoid confusion, the fourteen positions of the the cams aihxed diagram by the diagrammatically when the contour is high, the correthereto, are designated in the corresponding roman numerals. The contour of cam I44 is so conformed that switch I48 controlled thereby will be closed when the cam attains positions II, V, VIII, XI, XIII, and XIV. The contour of cam I45 is so conformed that switch I49 controlled thereby will be closed when the cam attains positions In, VI, IX, XII, XIII, and XIV, and open in all other positions. The contour of the cam I46 is so conformed that switch I50 controlled thereby will be closed when the cam attains positions IV, V, VI, X, XI, XII, XIII, and XIV and open in all other positions. The contour of cam I41 is so conformed that switch I5I controlled thereby will be open in all positions from I to VI, inclusive, and closed in position VII and all succeeding positions.

In considering operation of the control system of Fig. 2, it may first be assumed that the pressure in the conduit I29 is within the required control zone, and that the shaft I36, with the various control elements carried thereby, is at rest in position I, as shown in Fig. 3. Under this condition the switches I48, I49, I50, and I5I will corresponding pumps at rest; limit switch I4I will be opened and limit switch .142 closed. The fact of switch I4I being open makes it impossible for a circuit to be completed through the "high contact I34 of the controller I39 of the motor I31, thus precontrol point while the four pumps are at rest.

It may now be assumed that thepressure the conduit lZQ fallst'o-an extent that contact I32. in the-gauge I36 engages the-low contact I33. A circuit will thus be completed from the positive bus I55 through said contacts, and conductor I57, winding- I38 in the motor I31, conductor I58, and thelimit switch M2; to the negative bus I56, thus causing the motor I31 to operate and to rotate the shaft I35 in a sense to cause the several control" elements to assume position II as seen' in- Fig. 3 In this position the limit switch I'4I- will be closed, rendering it possible for the motor tobe operated in a sense to return the control element to position 1. Switch I52 will remain closed. Switches I49, I50, and I5lwill remainopen. Switch I i-8 will be closed, allowing the pump motor I24 to be energized through conductor IS'I, thus putting pump A into operation; and rendering available a flow of 50=gallons per'minut'e.

Should the flow available from the pump'A be sufficient to bring the pressure in the conduit I29 within the required range, thecontacts I32 and I33 wi'll be separated and the control mechanism brought to rest. Should the pressure remain'below the control point, the motor I3 'I will conti'nue to' operate, advancing theshaft I3'6'and the control-elements carriedthereby until position III is' attained. Inthis position, switch- I48 will be opened and switch I49 cl'osed', thus'bringin'g pump A to rest and placing pump Bin operation, rendering available a flow of 150 gallons per minute.

Shouldthe flow available from pump B be insufiicient to bring the pressure up-to the desired value, the control apparatus will continue to operat'euntil positi'onIV is attained, at which position switch I49 will be opened bringing pump B to rest; and at the same time cam- M6 will close switch- I50, energizing motor I26 and placing in service pumpCwith its available capacity of 200 gallonsper minute. Upon a further demandfor flow; as: indicated by the contacts I32 and I33 in gauge l3'llrremaining in engagement, the control mechanism will be advanced to position V, allowing' pump-G toremai'n on the line, and again closing-switch I48 and placing pump A in service, thus rendering available the combined capacity of" the-two units, or a flow of 250 gallons per minute. Thus, as thedemand' f'orincreased'capacity continues, the camshaft I36 will continue to advance,- causingpumps to'be added to, and taken from, the system in combinations as shown in Fig. with increasing capacities, until the final combination represented" by position XIII is attained. Under this condition all pumps will be operating, giving atotal fiow'of'800 gallons per minute. A continued low pressure condition-will cause the control apparatus to be moved to the position XIV, where the limit switch I iZwill be opened, making it impossible for any further advanceon the part ofthecontrol elements to be effected".

In' the event of the pressure in the system rising above the control point, the contact I32 in the instrument I- will be brought into engagement with the high contact I34, and the winding: I39 of the motor I3T energized through the conductors- I59 and i fili and-the limit switch causing. the motor to rotate the shaft I36 and the control elements carriedlthereby in a reverse sense to thatiherei-nbefore described, causing the cam shaft". to attain successive positions in a. reverse order, and; thus; effecting successive combinations of; pumps in. an: orderof decreasing" capacity: It will: be obvious. that at any time a condition: of

equilibrium is attained, so that the desired pressure is held in the conduit I29, the contact I32 in the gauge I30 will be cleared from both the contacts I33 and I34 and the controlling mechanism brought to rest in a position corresponding to the desired condition. Thus, with a suitably chosen combination of pump ratings, it ispossibleto attain a control which will-automatically select from said ratings a combination of pumps best suited to meeting the demand for'the liquid being handled thereby, and will" do this with a minimum deviation of the line pressure irom the value at which it is desired that said pressure be maintained.

It is'nct the intention to limit the'scope of the invention; to a group'of pump ratings or: timing schedules as specified in the foregoing description: The inventionisapplicable to any number. ofpumps or similar-units, andtoany desired'combination ofiratings, While the cams withwhich the form of the invention. shown in Figs..2 and 3 isprovided, are: shown as having their contours conformedto-a: specific arrangement, these may be-changed inany manner which may be found expedient. Furthermore, the cams maybe designed: to'have their contours adjustable, either by. the:- use of circumferentially movable sectors similar to the form shown in U. S. Letters-Patent 1,959,336, issued to F. J: Bast, May 22; 1934; or by the use ofremovable andreplaceable sectors-as shown inU. S- Letters Patent 2,096,182,. issued to. WI J. Kerr et al., October 19; 1937. Since these expedients are obvious and. form no part of, the present invention, they arenot described infurther detail. in this disclosure.

It willbenotedthat in. the above described embodiment, of. Figs. 2 andthetimeintervals between. successive actuations of contacts IliS--I5I are established by. the speed of rotation of the armature of. the constant-speedmotor I3! which drives, the cam shaft I35. Should it be found desirable to obtain increased time delay in the operation ofjsaidlmotor, such may be obtained by the addition of relays similar to therelays 5| and 51 shownin Eig. 1. These relays may be connected in a manner similar to that shown. in Fig. 4', which represents a connection system by which relay 4| of Fig. 1 may be incorporated in the circuits shown in Fig. 2. The contacts 44 and-45of saidrelay are connected respectively to the positive bus I55 and the winding I38 of the motor [37. Theactuatingelements of the relay are connected between the low contact I33 of the gauge I30 and the negative bus I56. An identicalsystem of connection is adaptable to incorporation of a similar relay into the circuit of the high contact of said gauge and of the winding it!) ofsaid motor. Upon closing of either of saidcontacts, the corresponding relay will be energized; and will act to delay the completion of the motor circuit until after the lapse of the pro-established time interval; after which the cycle control motor I 3'! will be energized andthe control cycle carried out ashereinabove described. Should the circuit remain closed at the contact I33 after the closing of the contacts 4'4 and tfi; the clutch will slip while the timer motor continues-to run; and this condition will continue untili the contacts of the pressure gauge have been opened.

The terms andexpressions which we have employed are used as terms of descriptions and not of limitation, and we havenointention, in the use of'suchterms and expressions, of excluding any equivalentsv of; the features shown and, de-

scribed or portions thereof, but recognize that various modifications are possible within the scope of the invention claimed.

We claim:

In combination, a plurality of devices operable to maintain a fluid pressure within a predetermined zone of values, gauging means responsive to said pressure and having electrical contacts operated when the pressure value passes outside said zone, a normally deenergized control relay having contacts in circuit with the first mentioned contacts when said control relay is deenergized, timing means in circuit with the contacts of said gauging means and with the said control relay contacts for energization when the contacts of said gauging means are operated and said control relay is deenergized, connections controlled by said timing means for causing said control relay to be energized at the end of a predetermined interval followin energization of said timing means with resultant disestablishment of the connection between said control relay contacts and said timing means, means for deenergizing said control relay at the end of a predetermined time following energization thereof for reestablishing said connection between said asaaoss control relay contacts and said timing means, means comprising a stepping relay and contacts brought into action upon successive operations thereof for bringing difierent ones of said devices into action to affect the value of said condition, and means comprising contacts controlled by said control relay for operatin said stepping relay successively upon successive energizations of said control relay.

ROBERT D. COWHERD.

WILLIAM H. STAHL, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,009,400 Fordyce et al Nov. 21, 1911 1,972,812 Wooley Sept. 4, 1934 2,080,232 Rogers et al May 11, 1937 2,222,595 Regester a- Nov. 26, 1940 2,223,415 Groves Dec. 3, 1940 2,246,940 Hood June 24, 1941 2,275,502 Broadhurst Mar. 10, 1942 2,312,728 OHagan et a1. Mar.2, 1943 

